Under the pressure of high interest rates, economic activity will decline at a seasonally adjusted annual rate of one-half percent in the current quarter, the second consecutive quarterly decline, government officials said yesterday.

The unpublished estimate, put together for internal government use by the Commerce Department, confirmed the evidence of other recent statistics that the economy may have entered a period of recession.

Separately, in the second regular revision of the data, the Commerce Department reported that the nation's output of goods and services, after adjustment for inflation, fell at a 1.6 percent annual rate in the second quarter. Originally the decline was put at a 1.9 percent rate, but in the first revision last month that number was raised to 2.4 percent. Real GNP rose at an 8.6 percent rate in the first three months of the year.

The so-called flash estimate for the current quarter is subject to substantial revision as more information becomes available. Other statistics indicate that outlays for personal consumption probably have fallen slightly in the third quarter. Housing construction is down significantly. Industrial production fell in August somewhat more than it went up in July.

On balance, the economy is moving sideways, with little prospect of a severe recession, most Reagan administration economists believe. That view is generally echoed by private forecasters.

Nevertheless, so long as interest rates stay at very high levels, the economic stagnation may continue. Forecasters are divided over whether real output will shrink or expand, but several economists recently have revised downward their estimates of growth for the final quarter.

Short-term interest rates, particularly for government securities, have dropped several percentage points in recent weeks. The Federal Reserve has encouraged this decline by providing additional reserves to the banking system to allow faster growth of the money supply, which has fallen below the Fed's target range.

The Fed reported yesterday that the measure of the money supply known as M1-B, which includes currency in circulation and checking deposits at finan cial institutions, rose $1.1 billion in the week ended Sept. 9 to a total of $432.9 billion.

In reporting the further second-quarter revisions, the Commerce Department said the decline in real output was due to a 4.7 percent drop in final sales. Part of that drop was offset by a sharp increase in the accumulation of business inventories during the quarter.

The increase in the GNP deflator was moved downward from the 6.6 percent annual rate reported in the first revision to 6.4 percent. The initial report for the quarter showed the deflator rising at a 6 percent annual rate.

Corporate profits from current production fell $12.7 billion to a seasonally adjusted annual rate of $190.3 billion, according to revised estimates, the department said. That is $3.3 billion higher than the initial estimate.